In one type of conventional magnetic separator, separation takes place in a magnetic matrix made of steel wool, expanded metal or similar material disposed in a canister. The canister is surrounded by an electromagnetic coil and the entire assembly is enclosed in a magnetic return frame. The magnetic field produced by the coil extends through the matrix in the same direction as the fluid flow. Feed is delivered at one end and the product of the separator is removed at the other end. There may be more than one matrix in the canister and each matrix may have more than one inlet and outlet.
An important consideration in such separators is that the matrix be delivered feed to be separated and the product of the separation be recovered in a manner to promote uniformity of the separation process: each unit area of the matrix should process the same amount of flow per unit time. This can be extremely difficult when, as is often the case, the matrix itself is not of uniform density and impedance to fluid flow. The problem is compounded by the use of only one or a few inlets and outlets per matrix, for that contributes to the non-uniformity of feed delivery and product recovery. Enlarging the space between the end of an inlet or outlet pipe and the matrix to create a reservoir of feed or product to improve uniformity unfortunately also may considerably reduce flow velocity and result in settling. In addition, increasing that space increases the corresponding dimension of the return frame, a substantial factor in separator cost, and increases the length of the air/fluid gap in the magnetic field thereby reducing the magnetic circuit efficiency. Often the input and output apparatus for such a magnetic separator is made integral with and often is a machined portion of the canister and/or frame, and must be tailored to meet the mechanical and hydraulic conditions associated with each matrix served.